The present invention relates to a speech synthesizing apparatus for synthesizing a speech signal based on speech data stored in a memory.
Conventional techniques of synthesizing speech based on digital data read out from a memory including analyzing-synthesizing methods are known which include linear predictive coding (LPC), partial autocorrelation coding (PARCOR), line spectrum pair coding (LSP), formant coding and the like.
When human speech is synthesized by one of such techniques, speech synthesizing conditions are preset which relate to the length of a speech frame (the period during which a speech signal can be regarded as stationary), the bit rate/frame, bit allocation for each analyzed parameter, the number of stages of a digital filter, and the like. When these speech synthesizing conditions are preset, the following synthesizing conditions can also be preset: the type of a sound source, presence of vocal tract loss, repetitive use of a parameter, the kind of voice (male or female), change in setting a frame length, interpolation of a parameter, the type of tone (speech or melody), setting of pitch (internally generated or externally determined), and an operation method such as a method for rounding the result of calculation.
Other conventional speech synthesizing techniques and waveform coding methods are also known which include adaptive delta-modulation (ADM), delta modulation (DM), adaptive difference pulse code modulation (ADPCM), adaptive predictive coding (APC) and the like. In such techniques, the sampling frequency, bit allocation and the like must be preset as speech synthesizing conditions.
In a conventional speech synthesizing apparatus, prior to speech synthesizing of each phrase, necessary speech synthesizing conditions are preset by a controller, such as a microcomputer, or are manually entered through a keyboard externally connected to the apparatus.
FIG. 1 shows an example of a conventional speech synthesizing apparatus of this type. The apparatus has a control 2, a memory 4 for storing speech data, an address counter 6 for designating an address of the memory 4, a condition memory 8 for storing synthesizing condition data, a parallel-serial (P/S) converter 10, and a synthesizer 12. The control 2 sets in the address counter 6 top address data corresponding to the first speech data of a phrase to be synthesized and also sets the corresponding condition data in the condition memory 8. Thereafter, the control 2 supplies a speech generating instruction to the synthesizer 12. In response to the speech generating instruction, the synthesizer 12 generates a data request signal or pulse train to the P/S converter 10. For example, this data request signal is obtained by passing a reference clock pulse through an AND gate connected to receive a pulse signal which is set high for a predetermined period in each frame period. Then, one-word speech data of n-bits is supplied in parallel to the P/S converter 10 from the memory location in the memory 4 which is designated by an address signal from the address counter 6. The n-bit speech data from the P/S converter 10 is serially supplied to the synthesizer 12. The synthesizer 12 synthesizes a speech signal using the speech data sequentially supplied from the P/S converter 10 in accordance with the synthesizing condition data stored in the condition memory 8.
Upon counting the n drive pulses included in the data request signal, an n-scale counter 14 supplies a pulse to the address counter 6 so as to increase the content of the address counter 6 by one count. Thereafter, the synthesizer 12 continues to generate drive pulses so as to synthesize a speech signal using the subsequent n-bit speech data supplied from the memory 4 through the P/S converter 10. In this manner, the synthesizer 12 counts up by one the content of the address counter 6 and simultaneously synthesizes a speech signal based on the speech data read out from the memory 4 for each word, while the resultant speech signal is supplied to an electric-acoustic converter (not shown).
In the conventional speech synthesizing apparatus as described above, the control 2 is required to set the synthesizing condition data in the condition memory 8, to set the top address data for designating the initial memory location storing the speech data of a selected phrase, to supply the speech generating instruction to the synthesizer 12, and so on. However, in a general microcomputer for controlling the control 2, the speech synthesizing function is a subfunction, and the control function is the main function.
The main function of a microcomputer is, for example, temperature control in an air conditioner system, high frequency output control in an electronic oven, and accurate delivery discrimination of various goods upon insertion of money by a customer in an automatic vending machine. Accordingly, when complex control such as phrase editing or the like must be executed by the control 2, the work loads of the control 2 and the microcomputer for setting predetermined synthesizing condition data therein are significantly increased.